Hi Jim:
The majority of telephone equipment (answer
machines, modems, fax, ect.) has filtering in it to
bypass RF. The bypass capacitance in these things
causes the higher frequency components of the audio
to be rolled off. This bypassing also kills DSL
signals. The devices that you install to make your
lines DSL ready, should be called blockers instead of
filters, because they have inductors in series with
each line that will keep the higher frequency
components of any signal on the line, while stopping
it from reaching the other telephone equipment.
Obviously the connection that is to be used for the
DSL modem must not have a blocker on it or the HF DSL
signal will not reach the DSL modem. My house wiring
was to weird to deal with so I installed a splitter
outside at the TELCO block and put one blocker there
for the house telephone equipment and ran a separate
line to the place where I wanted the DSL modem to
be. This way I didn't have to worry about all the
stuff in the house. You probably could have
unplugged all other telephone equipment in the house
except your computer modem and the connection rate
would have been better as well. I don't think that
matching Z on the phone patches is very important.
As a mater of fact I think the phone patch should
represent as high Z as posible to the phone line so
as to not load it down. But equilization is very
important as is balance and isolation from ground to
prevent common mode hum.
Good Luck
John, WA5BXO
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:amradio-
[EMAIL PROTECTED] On Behalf Of Jim candela
Sent: Tuesday, May 20, 2003 10:36 PM
To: [email protected]
Subject: [AMRadio] Telephone line bandwidth for AM
Phone Patch
All,
This is a little off subject, but just a
little. Sometimes when we
use a phone patch on AM, we can get better results
matching phone line
impedances, and maybe a little lead, or lag to help
equalize (or add
pre-emphasis) to the available bandwidth. I am sure
this was studied years
ago when professional baseball games were broadcast
from the announcer's
booth, and then piped for hundred's of miles down
telephone lines, and then
using the remoted audio to modulate broadcast AM
transmitters.
This all occurred to me today when I made my
house DSL ready. Four
lines (with a common beginning) now each have a DSL
filter at the end before
going into a telephone, or modem. I have NEVER been
able to connect to the
internet at a rate higher than 28.8 Kbs. Today after
installing DSL filters
(including one at the computer modem), my connection
is 48.8 kbs!!!! I just
might cancel the DSL which starts tomorrow, and keep
the filters. So what
technology is in use with these filters? How do they
apparently result in
improved connection speeds? Is it terminating the
line in it's
characteristic impedance, or increasing the
longitudinal balance?
Remember the answers to these questions need
to be discussed in a
manner that will help us AM hams have more fidelity
when we remote our
stations, or use a phone patch, or download the
AMRADIO reflector's email.
Regards,
Jim candela
WD5JKO
